A conventional chaining thread sew-in device attached to an overlock sewing machine for a chaining thread holder/cutter integrally comprising a knife and a pinching member made of elastic material disposed on a working face at an upstream side of the needle location, in which the operator brought the chaining thread created upon completion of sewing, together with the cloth, to the upstream side to press against the knife so as to cut by its cutting edge, the free end of the cut-off chaining thread pinched by the pinching member. The chaining thread left over at the machine side was held on the upper surface of the throat plate, and this chaining thread was sewn into the stitches of the next cloth, so that ravel of the stitches at the starting part could be prevented without any particular bar tacking process.
In such a chaining thread sew-in device, however, in order to cut the chaining thread consecutively produced from the cloth, the operator must move the cloth toward the upstream side of the needle location every time sewing of one cloth is over, which created a bottleneck with respect to improvement of job efficiency or automation of operation.
Accordingly, U.S. Pat. No. 4,149,478, it has been proposed to suck the chaining thread consecutively with the seams formed on a cloth into a suction tube behind the needle location, cut the chaining thread by the cutter provided in the opening of this tube by leaving a specified length from the machine side, move the free end of this chaining thread continuously from the machine side toward the front side of the needle location by air pressure, suck the free end of the thus transferred chaining thread by the suction part at the free end of the chaining thread, and operate the chaining thread pinching part disposed on the working face of the cloth plate so as to pinch the free end of the chaining thread.
In the conventional devices such as disclosed in U.S. Pat. No. 4,149,478, however, since the chaining thread pinching part and suction part of the free end of the chaining thread were disposed on the working face, this chaining thread pinching part disturbed the cloth feed, and job efficiency was often lowered.
Still, in the conventional devices, since the length of the chaining thread sewn into the seams of cloth was determined by the cutting position of the cutter disposed in the opening of the suction tube, it was difficult to change the length of the chaining thread to be sewn in depending on the products.